fmthola
commented
4 months ago I am having the same issue. After trying to fix the wiring, changing GPIO pins, it still wasn't resolving the issue.
I gave up, and just wrote a python script that would read the dmesg and I would parse it myself.
In your example: [ 193.956733] dht11 humidity-sensor: Don't know how to decode data: 42 0 31 3
42 is the humidity and 31 is the temperature (in C)
The code below only returns the humidity. WIth my sensor, I was getting values that would be 100+ the number. In your example, I would have values that would say 142 instead of just 42. There is logic in this code of if it's greater than 100, it will just ignore and try again.
Program flow:
- I have python open the /sys/bus/iio/devices/iio:device0/in_humidityrelative_input file, this creates an error, however that creates the dmesg error
- wait a moment after reading the file so dmesg has the log
- read the dmesg log files
- show only the most recent file
I know this is a hacky workaround. For my other application, I then simply imported and called this file to get the humidity
import subprocess
import time
import re
def read_humidity():
try:
with open('/sys/bus/iio/devices/iio:device0/in_humidityrelative_input', 'r') as file:
humidity = file.read().strip()
return humidity
except Exception as e:
# Do not print the error
return None
def get_dmesg_messages():
try:
# Capture the output of dmesg
result = subprocess.run(['dmesg'], stdout=subprocess.PIPE, text=True)
# Return the output as a list of lines
return result.stdout.splitlines()
except Exception as e:
print(f"Error reading dmesg: {e}")
return []
def filter_dht11_messages(dmesg_lines):
dht11_messages = []
pattern = re.compile(r"dht11.*Don't know how to decode data:")
for line in dmesg_lines:
if pattern.search(line):
dht11_messages.append(line)
return dht11_messages
def extract_first_number(message):
match = re.search(r"decode data: (\d+)", message)
if match:
return int(match.group(1))
return None
def main():
last_dht11_message = None
last_extracted_number = None
while True:
# Read humidity
humidity = read_humidity()
if humidity is not None:
print(f"Humidity: {humidity}%")
# Wait for 0.1 seconds
time.sleep(0.1)
# Get the dmesg messages
dmesg_lines = get_dmesg_messages()
# Filter for DHT11-related messages
dht11_messages = filter_dht11_messages(dmesg_lines)
# Extract the most recent message if there are any new ones
if dht11_messages:
most_recent_message = dht11_messages[-1]
if most_recent_message != last_dht11_message:
last_dht11_message = most_recent_message
extracted_number = extract_first_number(most_recent_message)
if extracted_number is not None and extracted_number <= 100:
last_extracted_number = extracted_number
# Print the most recent extracted number
if last_extracted_number is not None:
print(f"Most recent extracted number: {last_extracted_number}")
else:
print("No valid number extracted from DHT11 messages.")
# Wait before the next iteration
time.sleep(2)
if __name__ == "__main__":
main()
ashley-b
VDV2000
pelwell
Describe the bug
I think DHT11 module doesn't work with my kernel image
Steps to reproduce the behaviour
My aim is to read dht11 from the file system (kernel module) Steps :
ls -l /sys/bus/iio/devices/iio:device0is :It shows
dmesg | tailisadafruit-circuitpython-dhtand it worked fine (following that article https://pimylifeup.com/raspberry-pi-dht11-sensor/)Device (s)
Raspberry Pi 4 Mod. B
System
cat /etc/issue:cat /etc/rpi-issue:vcgencmd version:uname -m:Logs
Additional context
It may be irrelevant. But I am also appended lcd and i2c-gepio-expander to my rpi device tree to work with the modules. Both of them work fine.